What, exactly, is flour?

The most common way of classifying wheat flour in North America are terms such as whole wheat flour, bread flour, all-purpose flour, pastry flour, etc. This is a simplified system designed to indicate the best use of each flour. Want to make a loaf of bread? Use bread flour. Making pastry? Use pastry flour. Want a flour that you can use for a variety of things? Grab some all-purpose. And on the surface this seems pretty straightforward, but it's important to note that these are essentially marketing terms. While there are regulatory bodies that govern classification, there are no strict definitions to differentiate between say all-purpose flour and bread flour.

What you have instead are general ranges that are mostly tied to protein content. And while total protein can be an indicator of potential gluten strength, there are other factors which also determine a flour's suitability for a specific application. For example, there are all-purpose flours milled from soft wheat which are not suitable for bread making, but there are also some all-purpose flours that are actually stronger than some bread flours. In fact, the same exact flour might be labeled as all-purpose by one company, and as bread flour by another.

So what does this mean in terms of choosing the flour that's right for you? It means that in order to make that determination, there are more factors to consider. Let’s go over the different types of wheat, along with other factors that determine flour suitability. 

Types of Wheat

North American wheat is typically understood to be the strongest in the world. This is due to not only the types of wheat that are primarily grown, but also to the climate and methods of farming. But stronger doesn't necessarily mean better. In fact, artisan bakers often tend to favor wheat with more moderate strength because it yields bread with a softer, more tender crumb structure. Modern and heritage, or heirloom, wheat varieties are all descended from a trio of grains known collectively as the Farro grains – Emmer, Einkorn and Spelt. In the simplest terms, wheat is divided into red wheat or white wheat, and either hard or soft, so named because of the color and hardness of the kernel hull.

Hard Red Spring Wheat

Typically the strongest wheat due to both high protein content, and a protein distribution which yields strong gluten formation.

Hard Red Winter Wheat

The difference between Spring and Winter wheat is down to when it is planted. Winter wheat is planted earlier than Spring wheat, but actually yields slightly lower overall protein levels.

Hard White Wheat

These are primarily winter varieties, although they can be planted in Spring also. They typically have slightly lower protein levels than red wheat, and a milder flavor due to lack of tannins in the kernel husk.

Soft Red Winter Wheat

This type of wheat has much lower gluten content and a softer texture, making it ideal for cookies, crackers and other pastry applications.

Soft White Wheat

Similar to soft red wheat, these wheat varieties typically have low gluten forming potential, but with a milder flavor profile.

Durum Wheat

Durum is actually the hardest of all the wheat varieties, and has a protein distribution ideally suited to pasta making, since it produces a very extensible dough without much strength.

It is worth noting that this is a general overview. Due to diversity in breeding and genetics, as well as differences in both climate and methods across various wheat growing regions, there are varieties or cultivars of wheat which fall outside of these definitions. Historically, lighter wheat of medium hardness has been grown throughout Europe, while darker and harder varieties tend to proliferate in North America. Additionally, mills in Europe are increasingly importing hard Spring wheat from North America, and farmers on both sides of the pond are planting and harvesting seed imported from abroad. In short, outliers abound in the wide world of wheat.

Grist for the Mill

So now that we know more about wheat varieties, let's talk a bit about milling. There are many ways to mill wheat into flour, but the two main forms are roller-milled and stone-milled. Roller-milling passes wheat kernels between two rollers which are just narrower than the width of the kernel, thus separating the starchy endosperm from the bran and germ. The fractions are then separated into streams and passed through other rollers to further refine it, before being recombined in a variety of ways for various flours. In the case of stone-milling, the kernels are passed between two stones, a bed stone and a roller stone, and the resulting flour comes out in a single stream. Stone milled flour can also be refined through a sifting process called bolting after it has been milled.

For centuries, stone milling was the sole means of grinding grain into flour. Usually water or wind powered, these mills were ideal for the softer wheat varieties that were so prevalent throughout Europe. In the 18th century, the predecessor to the modern roller mill was developed in Hungary, and this method of milling quickly grew in popularity in Europe. This technology was then combined with designs for automated milling and cleaning of the grain to produce an improved version in the late 19th century. This allowed for more efficient refining of grain into patent (white) flour, and more effective milling of harder wheat varieties that were being grown in the Midwest and Eastern Europe.

Today, stone-milling has seen significant advancements as well, and this method is still preferred by many artisan bakers due to the flavor and texture that stone milled flour produces. Modern stone mills are capable of milling very fine flours from even harder varieties of wheat, but are typically favored for whole grain or high extraction milling rather than patent flours.

Now let's look a bit more closely at the characteristics of flour. The type of wheat(s) selected and the method of milling the grain ultimately result in a set of characteristics for the resulting flour.

Flour Characteristics

Absorption Rate

The absorption rate of a flour is the amount of water it will absorb to make a medium consistency dough. There are many factors which affect the absorption rate, such as gluten-forming protein content, protein distribution, particle fineness, percentage of whole grain present and amount of starch damage.

Generally speaking, flour made from stronger wheat will have a higher absorption rate than flour made from weaker wheat. And the finer the particle size, the greater the surface area, thus pointing to a higher absorption rate. Whole grain and higher extraction flours typically have a higher absorption rate than their more refined counterparts, all else being equal.

Protein Content

Protein is often used as the principal indicator of a flour's strength. And while it is generally true that higher protein wheat flour is stronger, this is not always the case. There are two gluten forming proteins, glutenin and gliadin, but they behave quite differently. The glutenin protein is responsible for elasticity (strength) in dough. The gliadin protein is responsible for a dough's extensibility (ability to stretch). Both these characteristics are necessary to produce a balanced dough, but the amount of one protein relative to the other will have an impact on how elastic or extensible the resulting dough will be.

In addition to protein distribution, protein quality is also a determining factor, and the quality of protein comes back to the genetics of the wheat, and the manner in which it is grown. Flour milled from a high protein wheat that has a lower quality of protein will perform more poorly than flour milled from a lower protein wheat of higher protein quality.

Extraction Rate

Extraction rate refers to the percentage of whole grain in flour. The higher the extraction rate, the greater the amount of whole grain present in the flour. Whole wheat flour is therefore 100% extraction, whereas 85% extraction flour has 15% of the total weight sifted out from the resulting flour. This sifted portion is mostly bran, but some of the germ and endosperm may also end up in the sifted fraction too, depending on method of extraction.

High extraction flour will generally have slightly higher protein content than sifted flour, since the bran portion of the grain consists mostly of fiber and protein, with relatively low starch. But the bran fraction also interrupts gluten bonds from forming, and its greater density tends to weigh down dough made with greater amounts of whole grain. This will generally mean the resulting bread will be denser, heavier, and with less overall volume than dough made from refined flour.

Starch Damage

It is generally understood that some amount of starch damage during milling is beneficial in terms of flour quality, but too much damage can also have negative effects such as making the resulting dough overly sticky. Although it is impossible to measure the amount of starch damage in flour yourself, harder wheat with higher protein levels will generally yield flour with a greater amount of starch damage.

Dough Rheology

Dough is a viscoelastic material, displaying both the properties of a solid and a fluid. It exhibits a viscous (fluid-like) and an elastic (solid-like) behavior when a force is applied to it. Gluten-forming proteins and polysaccharides, once hydrated and thoroughly mixed, are responsible for this viscoelastic nature.

Rheological properties of dough (also known as handling properties):

• Elasticity: the degree to which a dough will attempt to regain its original shape after a deforming force has been removed.
• Extensibility: ability of dough to stretch or deform. Dough should have enough extensibility (and minimal elasticity) to yield significant dough expansion during proofing and baking.
• Tenacity: this resistance to deformation is equivalent to “dough softness.” Dough should have as little resistance to deformation as possible.
• Stickiness: Ability of the dough to stick to the surfaces which they come into contact with. Dough needs some stickiness to be properly shaped and conveyed during handling. The simplest way of modifying the stickiness of dough is by increasing or decreasing the amount of water in it.

Bringing it all together

This is perhaps the most challenging part of understanding flour, because it relies on qualitative assessment from the baker. And that takes practice. But with time and repetition, one begins to see the correlation between flour qualities, and the resulting dough made from them. The simplest of qualitative assessments to perform is a basic flour stress test.

This first involves feeling the dry flour with your fingers, and visually inspecting it. Is it whiter in color or more tan? Is the color consistent throughout or is it flecked or mottled? Does it feel soft and fine like baby powder or harder like sand? These answers will all provide clues as to how it will perform.

Then take a portion of the flour and add water to hydrate it to a set level, such as 70% hydration. Feel the resulting dough and assess it for elasticity and extensibility, then rest it for 20 minutes and perform the same test. How easily does it stretch? How far can you extend it? Does it tear easily? Is it soft or hard? Next, add 5% more water and perform the same test again. Then another 5%, and so on.

Now this test does not involve any fermentation, so it's not completely accurate, but it will give you a rough idea of the appropriate hydration level for a particular flour. It begins to give you an idea of the type of dough this flour will form at a particular hydration level, and the rheological properties that dough will have.

Further testing is needed to assess mixing tolerance and fermentation tolerance. In short, mixing tolerance is a measure of how well a particular flour resists over mixing when made into dough. Fermentation tolerance relates to how much fermentation a particular dough can take before the gluten structure begins to break down. In general, stronger flours tend to have both a greater mixing tolerance and fermentation tolerance than weaker flours, although this is not always the case.

Finally, assess the end product, which is the resulting bread. How well did the crust form? What is the crumb structure and texture like? Stronger flours will produce a dough capable of holding more water, but they will also yield a firmer, chewier texture in the end product. Weaker flours may absorb less water, but tend to yield a softer, more tender end product.

With a bit of practice, this information can be used to begin blending flours to achieve different characteristics in their bread. For instance, one might choose a medium strength flour as their base flour, adding a percentage of stronger whole grain for additional water absorption and flavor, while still yielding a more tender crumb, or using a portion of stronger flour to bolster a weaker flour chosen for its extensibility.